If it is slow on the internet, it is your internet provider that is the problem. Either you have slow speeds through them or are not getting the speed you should. If the computer is slow outside of the internet then the above link might help.

Dooles wrote:Guys, sometimes my MacBook Pro is running so slow (early 2015, sierra).
What can be the reason? And how can I fix it?

I have few Mac speed up tips. First of all, it's important to delete old apps or useless files. By the way, there are plenty of hidden files that can make your Mac slow. Also, you can use cleaning utilities.